As stated above, the answer can vary wildly. I've been running my own business for just over 4 years, and I typically charge on a project basis for well-edfined tasks (such as yours). The best way to come up with project totals, IMO, is to figure out hourly rate(s) for various activities (for example, admin/meeting time would be billed differently from creative) and use a project estimate spreadsheet.
The hourly rates, in turn, are based on how much you will need to make to survive. You have to factor in all expenses--health insurance, IRA contributions, materials, depreciation on equipment, whatever applies to your situation.
Starting a business is not hard. Keeping it afloat is (very), especially in this economy. Good luck with your new venture.